Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$179.62	4.285%	$187.3167	$187.32	$187.30	$187.30
Purchase #2	$170.30	3.836%	$176.8327	$176.83	$176.85	$176.80
Purchase #3	$156.35	13.756%	$177.8575	$177.86	$177.85	$177.90
Purchase #4	$115.32	3.467%	$119.3181	$119.32	$119.30	$119.30
Purchase #5	$94.51	11.862%	$105.7208	$105.72	$105.70	$105.70
Purchase #6	$78.91	9.131%	$86.1153	$86.12	$86.10	$86.10
Purchase #7	$175.43	11.854%	$196.2255	$196.23	$196.25	$196.20
7 purchase totals =	$970.44		$1,049.3866	$1,049.40	$1,049.35	$1,049.30